Conventionally, Group-III nitride semiconductors such as aluminum gallium indium nitride (AlXGaYInZN: 0≦X, Y, Z≦1, X+Y+Z=1) have been used, for example, as a light-emitting layer or clad layer of a light-emitting diode (LED), or an electron channel layer or electron supplying layer of a high mobility field effect transistor (TEGFET) (see, for example, Patent Document 1 and Non-Patent Document 1).
A device using the Group-III nitride semiconductor (Group-III nitride semiconductor device) usually has a heterojunction structure of Group-III nitride semiconductors to express the device function. For example, Patent Document 1 discloses an invention where the light-emitting part of LED or laser diode (LD) is constituted with the heterojunction of gallium nitride (GaN) and gallium indium nitride (GaYInZN: 0≦Y, Z<1, Y+Z=1).
The Group-III nitride semiconductor layer or hetero-junction structure comprising the Group-III nitride semiconductor layers, constituting a compound semiconductor device, has been heretofore produced by the vapor phase growth method mainly on a sapphire (α-Al2O3 single crystal) substrate.
However, the lattice mismatch, for example, between the sapphire substrate and gallium nitride (GaN) is as large as about 16% (see, for example, Non-Patent Document 2) and the gallium nitride layer formed on a sapphire substrate is known to contain a large amount of misfit dislocations exceeding 1×108/cm2 (see, for example, Patent Document 3). In the heterojunction structure comprising Group-III nitride semiconductors such as gallium nitride, the misfit dislocation propagates to an upper layer over the part of the heterojunction. Therefore, in conventional techniques, a heterojunction structure reduced in the dislocation density can be hardly obtained.
The present inventors had found that a boron phosphide (BP) layer is effective in inhibiting the propagation of misfit dislocation from the Group-III nitride semiconductor layer.
Patent Documents 2 to 7 disclose a technique of forming a light-emitting device by joining a boron phosphide layer on a Group-III nitride semiconductor layer comprising hexagonal wurtzite gallium nitride or the like. However, in these conventional techniques, inhibition of the propagation of misfit dislocation from the Group-III nitride semiconductor layer is not intended (see, Patent Documents 8 and 9). A crystalline structure for the boron phosphide layer effective in satisfactorily and stably inhibiting the propagation of misfit dislocation from a Group-III nitride semiconductor layer is not yet known. Therefore, a pn-junction structure of a Group-III nitride semiconductor layer and a boron phosphide layer, which is reduced in the leakage current and can express good rectification property, is heretofore difficult to stably obtain.
(Patent Document 1)
JP-B-55-3834 (the term “JP-B” as used herein means an “examined Japanese patent publication”)
(Patent Document 2)
JP-A-10-242514 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
(Patent Document 3)
JP-A-10-242515
(Patent Document 4)
JP-A-10-242567
(Patent Document 5)
JP-A-10-242568
(Patent Document 6)
JP-A-10-242569
(Patent Document 7)
JP-A-10-247745
(Patent Document 8)
JP-A-10-247760
(Patent Document 9)
JP-A-10-247761
(Non-Patent Document 1)
Isamu Akasaki (compiler), III Zoku Chikkabutsu Handotai (Group-III Nitride Semiconductor) (Advanced Electronics 1-21), 1st ed., pp. 285-293, Baifukan (Dec. 8, 1999)
(Non-Patent Document 2)
Isamu Akasaki et al., “EFFECTS OF AlN BUFFER LAYER ON CRYSTALLOGRAPHIC STRUCTURE AND ON ELECTRICAL AND OPTICAL PROPERTIES OF GaN AND Gal-xAlxN (0<X≦0.4) FILMS GROWN ON SAPPHIRE SUBSTRATE BY MOVPE”, (the Netherlands), Journal of Crystal Growth, Vol. 98, pp. 209-219 (1989)
(Non-Patent Document 3)
L. T. Romana et al., “STRUCTURAL CHARACTERIZATION OF THICK GaN FILMS GROWN BY HYDRIDE VAPOR PHASE EPITAXY”, (U.S.A.), Mat. Res. Soc. Symp. Proc., Vol. 423, pp. 245-250 (1996)